The present invention relates to absorbent paper products and, more specifically, to products made of cellulose cotton and suitable for sanitary and household uses. Essentially, the invention applies to toilet paper, however it also may be used for household purposes such as towels, hand towels, table napkins, handkerchiefs, etc., all being of paper.
In general, absorbent paper products consist of one or more superposed, cotton cellulose plies which can be interconnected.
As regards toilet paper, conventional products include two or three, even four joined plies.
More specifically, the present invention concerns a product of at least three plies and to a method of manufacture therefore.
U.S. Pat. No. 3,414,459 describes an absorbent paper structure of at least two plies. It also cites a product of three joined plies, a third ply being sandwiched between two embossed outer plies. This structure is based on plies of a specific surface weight of about 17 g/m2 for each ply. According to the manufacturing method described in this patent, the two outer plies are embossed separately with a salient pattern consisting of discrete protrusions. Each ply is made to pass between a metal cylinder engraved in relation to the desired pattern and a smooth rubber cylinder. Each ply so made in general is fitted with a repeat pattern 3 to 30 protrusions per unit area, here cm2.
As regards the three-ply structures disclosed in the above U.S. patent, the pattern density, that is the number of protrusions per unit area is about 11 protrusions/cm2.
The third and unembossed ply is sandwiched between the two embossed ones and, more specifically, it is configured between the distal areas, or tops of the protrusions of each ply. In other words, the protrusions point inward of the structure. The three plies are joined by being made to pass within the compression interval between two engraved metal cylinders each belonging to the outer plies"" embossing apparatus. The bosses of each engraved cylinder are configured to be mutually opposite each other. This joining technique in general is called xe2x80x9ctip-to-tipxe2x80x9d. In the above U.S. patent, the three plies are connected by applying a sufficiently high pressure to produce interfiber connections. No adhesive at all is applied to the distal areas of the protrusion patterns of the outer plies.
However, the manufacturing method described in the prior art patent entails rapid wear of the embossing cylinders because of the high compression which must be applied to join the three plies.
Furthermore, the structure described in the above U.S. patent is of low pattern density (about 10 to 15 protrusions/cm2). The three ply products with such structures are mainly intended for use as rags or paper towels that foremost demand mechanical strength and especially absorption. Accordingly, the embossings are comparatively deep and hence of low density.
Other absorbent paper products consist of three plies which are joined in a different way. Illustratively, there are products for which on one hand a set of two superposed plies are embossed, and on the other hand, a third ply, by two distinct embossing apparatus. The first two superposed plies as well as the third ply are embossed into salient patterns constituted of protrusions. The pattern density per se remains low, that is it is less than 20 protrusions/cm2 for this kind of product. The two superposed plies and the third ply are joined by a joining cylinder so that the distal areas of the protrusions of the two superposed plies are situated opposite the surfaces situated between two protrusions in the plane of the third ply. This technique is called xe2x80x9cnestingxe2x80x9d.
In the text below, the definition of xe2x80x9cnestingxe2x80x9d is extended to the case wherein the interconnection plane between the distal area of the protrusions of a first embossed ply and a second ply are situated in the same plane as the plane of the second ply regardless of the relative position of the distal area relative to the protrusions of the second ply. In this manner, the distal area might be situated between two protrusions of the second ply, however it also might cover in part or in whole one of these protrusions which is crushed thereby.
A combination procedure of this sort for three plies is described in the European Patent Application 0 570 578.
The procedure consists in separately embossing a first and a second ply, the second ply consisting of two superposed foils, by means of a first and a second embossing apparatus, the apparatus including an embossing pattern having a density less than 20 protrusions/cm2, in applying at least partly an adhesive to the tops of the protrusions formed into the first or second ply and in joining the two plies by means of an inelastic joining cylinder configured parallel to the engraved cylinders of the embossing apparatus, whereby their protrusions will nest. In this cylinder, the joining cylinder is kept biased against the engraved cylinder at a predetermined minimum distance.
The objective of the structure such as described in the European patent is to manufacture thick products offering a good xe2x80x9cfeelxe2x80x9d. However, and especially with respect to toilet paper, the comparatively coarse embossing entails mediocre softness. Also, powerful embossing is required to attain the desired substantial thickness.
Other compound products composed of three plies also have been disclosed.
Illustratively, European Patent Application 0 564 319 describes a product including three separately embossed plies which are consecutively joined. More specifically, small and large protrusions are embossed into a first ply. Protrusions on a second ply are made by separate embossing. The latter protrusions are mutually apart by the same distance as there is between the protrusions of the first ply, that is, at least by the height of a large protrusion of the first ply. Adhesive is deposited on the ends of the protrusions of the second ply and then a pad is made between the first and second plies by superposing the ends of the small protrusions of the first ply and the ends of the protrusions of the second ply in the tip-to-tip position, the large protrusions of the first ply nesting between the protrusions of the second ply.
The third ply is embossed separately and the pitch of this embossing is identical with that of the first ply""s larger protrusions. The tops of the third ply""s protrusions are coated with adhesive and this third ply and the pad between the first two plies are joined in such a manner that the third ply""s protrusion tops will be glued in the tip-to-tip position on the second ply at the level of the first ply""s large protrusions.
The product so made offers improved thickness and stiffness. On the other hand its comparatively complex structure requires several gluing stages. The method per se is fairly complex in implementation and entails a fairly complicated industrial facility.
Moreover, the above procedure allows manufacture of only embossed products having a pattern density less than 20 protrusions/cm2 and the thickness of the products so made and consisting of these plies will not be optimal.
Lastly a three-ply paper product which is both thick and soft, offers a good feel and is crush-resistant is known from French Patent Application No. 98 02792.
In the above application, the product includes two outer embossed plies each having salient patterns consisting at least in part of discrete protrusions pointing inward the structure, and a central ply. The plies are joined to each other by connecting the distal areas of at least part of the protrusions of each of the outer embossed plies to the central ply. This product is characterized by each of the outer embossed plies being bonded adhesively to the central ply and by at least one of the plies being fitted with a pattern density larger than 30 protrusions/cm2.
Also, one of the plies may include joined patterns, for example being at two different heights relative to the ply""s reference plane.
However, the joining mode between the different plies is the tip-to-tip type with all the drawbacks attaching to this junction mode.
The object of the present invention is palliation for the set of above cited drawbacks both as regards the products and their manufacturing procedures.
Another object of the present invention is to create a novel product constituted by at least three plies which are thick and soft, offer a good feel, and resist crushing once wound up in a roll.
The object of the invention is an absorbent paper product with a specific surface weight of approximately 36 to 105 g/m2 and including at least three plies, two outer plies (namely a lower and an upper ply) which are embossed and each bearing salient patterns constituted at least in part of discrete protrusions, and a central ply, the distal areas of at least part of the protrusions of each of the outer plies facing toward the central ply, and at least one of the outer plies having a pattern density larger than 30 protrusions/cm2, the lower embossed outer ply being fitted with a first and a second pattern, the second pattern being of a height less than that of the first pattern, characterized in that the central ply and the embossed upper outer ply are joined in a nesting manner with the lower embossed outer ply at the level of at least part of the tops of the first pattern of the embossed lower outside ply.
In surprising manner, such a structure combines greater softness and greater thickness. On one hand, fine embossing imparts great touch softness to the sheet""s outer surface and, on the other hand, it offers very good crush resistance. The latter property is enhanced by the central ply which precludes any nesting between the two outer plies, as would take place in the absence of the central ply, because such very fine protrusions would provide only tiny support areas.
Another object of the present invention is a novel product including at least three plies of the nested type and which is used as toilet paper, table napkins, handkerchiefs, rags or the like.
Still another objective of the invention is a fabrication method for an absorbent paper product including at least three bonded plies, each of a specific surface weight of about 12 to 35 g/m2, preferably 12 to 25 g/m2, characterized in that it involves:
embossing a first outer ply on an embossing cylinder including at least one salient pattern composed at least in part of embossing tips of height H1 to fit the ply with a first pattern of protrusions,
superposing a central ply on the protrusions of the first outer embossed ply,
embossing a second outer ply on an embossing cylinder including a salient pattern composed at least in part of embossing tips of height hxe2x80x21,
joining in the nested mode the first outer embossed ply fitted with the central ply to the second outer embossed ply by means of a joining cylinder, and
applying sufficient pressure to join the three above plies.
Other features and advantage of the invention are elucidated in the comprehensive description below and in relation to the attached drawings.